QCL Spectroscopy System and Applications Therefor

ABSTRACT

A spectroscopy system comprising at least two laser modules, each of the laser modules including a laser cavity, a quantum cascade gain chip for amplifying light within the laser cavity, and a tuning element for controlling a wavelength of light generated by the modules. Combining optics are used to combine the light generated by the at least two laser modules into a single beam and a sample detector detects the single beam returning from a sample.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/159,225 filed on Jun. 13, 2011, which claims the benefit under 35 USC119(e) of U.S. Provisional Application Nos. 61/354,136, filed on Jun.11, 2010, 61/410,231, filed on Nov. 4, 2010 and 61/475,053, filed onApr. 13, 2011, all of which are incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION

Grating tuned external cavity semiconductor lasers have been used forspectroscopy sources for many decades. Recently, wide band infrared gainchips have been available based on quantum cascade technology. Quantumcascade lasers (QCL) generate light in the mid to far infrared (IR)using intersubband transitions in a repeated stack of semiconductormultiple quantum well heterostructures.

SUMMARY OF THE INVENTION

In general, according to one aspect, the invention features aspectroscopy system comprising at least two laser modules, each of thelaser modules including a laser cavity, a quantum cascade gain chip foramplifying light within the laser cavity, and a tuning element forcontrolling a wavelength of light generated by the modules, combiningoptics for combining the light generated by the at least two lasermodules into a single beam, and a sample detector for detecting thesingle beam returning from a sample.

In embodiments, three of the laser modules are used and the tuningelement comprises a grating or a Fabry-Perot tunable filter.

Some applications require projection optics for projecting the singlebeam to a sample. A sighting laser and a housing with attached handleare also provided, wherein the laser modules are contained within thehousing.

In some embodiments, retroreflectors positioned in a room, wherein thesingle beam is projected to the retroreflectors and then returned to thesample detector.

In other examples, a gas cell is provided within a portable hand-heldhousing, wherein the laser modules and the vapor cell are containedwithin the housing, the single beam analyzing air in the gas cell.

One application uses a system for puffing air onto shoes and a systemfor collecting the air, the single beam analyzing the collected air. Amagnetometer can also be provided.

In general, according to another aspect, the invention features aquantum cascade laser microscopy system comprising the spectroscopysystem, wherein the sample detector comprises a detector array, a lightmicroscope for projecting the single beam onto the sample, and an X-Yscanning stage for scanning the sample under the microscope.

In general, according to another aspect, the invention features a methodfor detecting recently disturbed earth comprising scanning soil with aquantum cascade laser spectroscopy system from a stand-off distance,recording the absorption spectra of the scanned soil, establishing abaseline spectra of soil that has not been recently disturbed, anddetecting changes in the spectra consistent with recent disturbance ofthe soil.

Embodiments further comprise scanning the soil with ground penetratingradar.

The system can be deployed in a hand-held arrangement by an operatoron-foot, on an interrogation arm, or on unmanned aerial vehicles.

In general, according to another aspect, the invention features a methodfor testing a surface for contaminants in a pharmaceutical environmentcomprising directing emission from a quantum cascade laser spectroscopysystem towards a pharmaceutical surface at a stand-off distance,detecting an absorption spectra of the pharmaceutical surface using thequantum cascade laser spectroscopy system, comparing the absorptionspectra with a standard, and calculating a level of contaminants presenton the pharmaceutical surface.

In embodiments, the pharmaceutical surface is the interior of a reactionvessel. The method involves comparing the level of contaminants to apre-determined acceptable level and, if the level of each contaminant isnot below the acceptable level, cleaning the pharmaceutical surface andretesting the level of contaminants until it is below the acceptablelevel.

In general, according to another aspect, the invention features a methodfor identifying bacterial species comprising growing a bacterial culturein a sealed container, detecting an absorption spectra of a gaseousheadspace of the sealed container using a quantum cascade laserspectroscopy system, identifying a gaseous composition of the headspaceby analysis of the absorption spectra, and correlating the gaseouscomposition of the headspace with a presence of a specific species ofbacterium.

In general, according to another aspect, the invention features a methodfor monitoring biological or chemical reactions comprising connecting aquantum cascade laser spectroscopy system to a fiber optic probe,placing the fiber optic probe in contact with a chemical or biologicalreaction, detecting an absorption spectra of the reaction at multipletime points, comparing the absorption spectra to a standard, anddetermining the rate of the reaction.

In general, according to another aspect, the invention features a methodfor distinguishing between cell types in vivo, comprising connecting aquantum cascade laser spectroscopy system to a fiber optic probe,placing the fiber optic probe in contact with cells of a patient,scanning the cells with the fiber optic probe, recording the absorptionspectra of the scanned cells, comparing the spectra to a library ofspectral data, and determining cell type as a function of the spectraldata.

In general, according to another aspect, the invention features a methodfor testing composites for thermal damage comprising: detecting anabsorption spectra of a composite using a quantum cascade laserspectroscopy system, and identifying damage to the composite bycomparison of the absorption spectra to the spectra of the samecomposite without thermal damage.

In general, according to another aspect, the invention features aspectroscopy system comprising: an external cavity laser including alaser cavity, a quantum cascade gain chip for amplifying light withinthe laser cavity, and a tuning element for controlling a wavelength oflight generated, wherein the tuning element is resonantly tuned to scanthe wavelength of the light, a sample detector for detecting the lightreturning from a sample, and an accumulator that stores theinstantaneous response of the sample detector in a bin corresponding toa wavelength of the light.

In general, according to another aspect, the invention features a methodfor identifying chemicals on reflective surfaces comprising directingemission from a quantum cascade laser spectroscopy system towards areflective surface at a stand-off distance, detecting an absorptionspectra of the reflective surface using the quantum cascade laserspectroscopy system, comparing the absorption spectra with a spectraldata library, and identifying any chemicals on the reflective surface.

In embodiments, the Kramers-Kronig (KK) transform is applied to theabsorption spectra to remove specular distortions.

In general, according to another aspect, the invention features a methodfor identifying chemicals in pools of liquid comprising: directingemission from a quantum cascade laser spectroscopy system towards a poolof liquid on a surface at a stand-off distance, detecting an absorptionspectra of the pool of liquid using the quantum cascade laserspectroscopy system, comparing the absorption spectra with a library ofspectral data, and identifying any chemicals present in the liquid.

The above and other features of the invention including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described with reference to theaccompanying drawings. It will be understood that the particular methodand device embodying the invention are shown by way of illustration andnot as a limitation of the invention. The principles and features ofthis invention may be employed in various and numerous embodimentswithout departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the sameparts throughout the different views. The drawings are not necessarilyto scale; emphasis has instead been placed upon illustrating theprinciples of the invention. Of the drawings:

FIG. 1 is a scale plan drawing of a QCL spectroscopy system of thepresent invention;

FIG. 2 is a scale perspective drawing of a QCL spectroscopy system ofthe present invention showing parts of the housing and electronicsboards;

FIG. 3 is a flow diagram illustrating one mode of operation for the QCLspectroscopy system for non-interleaved spectral acquisition;

FIG. 4 is a flow diagram illustrating operation for the QCL spectrallyspectroscopy system for interleaved spectral acquisition.

FIG. 5 is a detailed view showing one configuration for the externalcavity configuration of the tuners 110;

FIG. 6 is a detailed view of a grazing angle probe;

FIG. 7 is a detailed view showing another configuration for the externalcavity grating tuner 110;

FIG. 8 shows the electronics for the QCL spectroscopy system using theresonant scanning mirror;

FIG. 9 is a plot of pulses as a function of wave number generated forthe resonant scanning grating tuning system;

FIG. 10 shows the electronics that enable the integrated pulse data tobe sorted into spectral bins;

FIG. 11 illustrates the temporal sampling of the sample detectorrelative to the pulse generated by the QCL;

FIG. 12 illustrates an alternative optical train design;

FIG. 13 shows a portable configuration of the QCL spectroscopy system;

FIG. 14 shows an alternative configuration of the QCL spectroscopysystem in which the QCL spectrometer system is used with an IR array toprovide a 2D “chemical image” of a surface;

FIG. 15 shows an alternative configuration of the QCL spectroscopysystem in which the QCL laser is separated from the detector fordetection of scattered contamination;

FIG. 16 shows an alternative configuration of the QCL spectroscopysystem in which the QCL spectrometer system is placed at a selectedlocation within a room and scans across a long distance by transmittingbeams across the room to retroreflectors that generate a return beam;

FIGS. 17A and 17B are perspective and top views showing an alternativeconfiguration of the QCL spectroscopy system that detects particles thatcome off of pedestrians' shoes;

FIG. 18 is a flow diagram illustrating a method for detecting disturbedearth using the QCL spectroscopy system;

FIG. 19 is a plot of surface reflectance as a function of wavelengthgenerated at varying angles of intersection of the laser with theground;

FIG. 20A illustrates a QCL Cassegrain optical system;

FIG. 20B is a plot of measurement time as a function of standoffdistance generated with varying collection optics;

FIG. 21 is a flow diagram illustrating a method for validating surfacecleanliness using the QCL spectroscopy system;

FIG. 22 is a flow diagram illustrating a method for identifyingbacterial species using the QCL spectroscopy system;

FIG. 23 is a flow diagram illustrating a method for monitoring chemicalreactions using the QCL spectroscopy system;

FIG. 24 shows a oral cancer diagnostic application for the QCLspectrometer;

FIG. 25 shows a oral cancer diagnostic QCL analysis system;

FIG. 26 shows common ATR Configurations;

FIG. 27 shows alternative IRE geometries;

FIG. 28A, FIG. 28B, and FIG. 28C respectively show three differentembodiments of the ATR probe tip;

FIG. 29 is a flow diagram illustrating a method for identifyingcancerous cells using the QCL spectroscopy system;

FIG. 30 is a flow diagram illustrating a method for identifying thermaldamage to composites using the QCL spectroscopy system;

FIGS. 31 and 32 show examples of hollow fibers that are used with theQCL spectrometer system;

FIG. 33 shows the coupling of the fiber probe to the spectrometersystem;

FIG. 34 is a schematic diagram showing implementation of the probe;

FIG. 35 is a schematic diagram showing implementation of the probe;

FIG. 36 is a schematic diagram showing implementation of the probe;

FIG. 37 is a schematic diagram showing implementation of the probe;

FIG. 38 is a block diagram of a QCL microscope;

FIG. 39 shows an alternative QCL tunable laser configuration in whichthe grating tuner is replace with a Fabry-Perot tunable filter and fourmicro electrical mechanical system (MEMS) Fabry-Perot tunable filterconfigurations;

FIG. 40 is a flow diagram illustrating an automated method foridentifying substances using the QCL spectroscopy system; and

FIG. 41 is a flow diagram illustrating algorithm methodology foridentifying substances using the QCL spectroscopy system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The system that is described herein is a Mid-IR Tunable Quantum CascadeLaser (QCL) based spectroscopy system. This system is capable ofobtaining absorption spectra of various materials for identification andanalysis. It operates by emitting a wavelength range that is within themid-IR fingerprint region (1500-900 cm−1) in a continuously ordiscretely tuned repeating packet. In one embodiment, the system hasmeasurement range of 6 to 12 micrometers, with current versions offering6 to 10 micrometers and 7 to 12 micrometers.

Traditionally, these types of measurements have been taken utilizingFourier transform infrared (FTIR) spectrometers working the mid-IR. AnFTIR spectrometer typically utilizes a broadband mid-IR source such as aheated black body source and a Michelson interferometer.

In contrast, the current system takes the same spectral measurementswith a tunable mid-IR laser and detector that correlates the outputsignal with the signal that is returned from the sample. Because thelaser can illuminate the sample with much higher power than the glowingblack body source of the FTIR spectrometer, there are several keyadvantages that this system has relative to an FTIR spectrometer. Theseadvantages include: faster measurements, more sensitive measurements dueto higher signal to noise ratios, and sensitive standoff measurementswhere measurements are taken of trace substances at a distance.

The combination of three key independent innovations enable QCL basedspectroscopy systems to take sophisticated spectral measurements. Theyinclude:

1. A widely tunable spectral range QCL assembly tunes across the mid-IRfingerprint spectral range, such as 6 to 12 micrometers. Previously,QCLs have been utilized in relatively narrow tuning ranges and have notbeen packaged together into a system that provides sufficiently wideranges to perform sophisticated spectral measurements. The describedsystem includes multiple laser tuner packages that are optically alignedto emit from the same exit optics and their emissions stitched together,spectrally, to achieve both a continuous and a wide tuning range.

2. Very rapid and repeatable laser pulses are tuned across the mid-IRfingerprint region. It provides high levels of repeatability in theamplitude of tuning range (good 100% line), low noise, rapid tuning, anda compact device.

3. Very fast electronics correlate the return signal with the emittingwavelength, so that it is possible to reconstruct the absorptionspectra. The absorption spectra are produced after either averaging orin near real-time.

The following provides more details on each of these three keyinnovations:

Widely tunable QCL Laser Assembly

The described system includes multiple laser tuner packages that areoptically aligned to emit from the same exit optics and their emissionsstitched together to achieve both a continuous and a wide tuning range.Each of the laser modules is combined together using a combination ofmirrors and dichroics, so that all of the beams exit through the samelaser output port. Each of the modules independently covers at least 100wavenumbers and usually covers 200 wavenumbers or more, in embodiments.The system with multiple modules combined together provides sufficientspectral range to do practical absorption spectroscopy.

Furthermore, these laser modules either scan through their completespectral range in sequence or their pulses are interleaved. When thetuners are interleaved, during the time that the first laser fires andthen turns off, the second laser fires and turns off, then the thirdlaser fires and turns off, and then repeats with the first laser firingagain. The advantage with interleaving is that it takes advantage of thedowntime in the duty cycle of each laser to minimize the time requiredto cover the full spectral range of all of the laser packages combined.

FIG. 1 shows a QCL spectroscopy system 100 which has been constructedaccording to the principles of the present invention.

It comprises an optical platform 105. Installed on the optical platform105 are multiple tunable QCL lasers 110A, 110B, 110C. In otherembodiments, more than three are installed together on the commonoptical platform 105.

The system in one example provides a nominal measurement range orscanband of 6 to 12 micrometers. Narrow scanning versions coverscanbands of 6 to 10 micrometers and 7 to 12 micrometers, however.

Each of the QCL lasers 110 includes a grating tuner 112. A QCL chip 116is installed on a submount. An external cavity lens 114 couples lightfrom the back facet of the QCL chip 116 to the grating tuner 112. Lightexiting the front facet of the QCL chip 116 is collimated by anextraction lens 118.

The emission from the first QCL laser 110A is reflected by a fold mirror120. A dichroic mirror 122 is reflective for the scan band of the secondlaser 110B but transmissive for the scan band of the first QCL laser110A and it is angled at 45 degrees with respect to the tunable signalsof both the first QCL 110A and the second QCL 110B. This generates afirst combined beam 123 including the tunable signals from the first QCL110A and the second QCL 110B. The combined beam 123 from the first andsecond QCL lasers is directed at a partially reflecting mirror 124. Theemission from the third QCL laser 110C is directed at the same partiallyreflecting mirror 124, with the partially reflecting mirror 124 beingangled at 45 degrees with respect to both the first combined beam 123and the tunable signal from the third QCL 110C. This results in a finalcombined beam 140 that includes the signals from all three QCL lasers110. Similarly, the emission from all three QCL lasers is also receivedby a reference detector 126 located opposite to the partially reflectingmirror 124.

In other embodiments, element 124 is a dichroic mirror that isreflective in the scan bands of QCL's 110A and 110B but transmissive tothe scan band of QCL 110C. In this case some residual light from allthree QCL's still reaches the detector 126.

The combined output beam 140 exits through an optical port and isdirected at the sample 132. In a typical application, the sample 132diffusely or specularly reflects the output beam 140. This light 141 iscollected by a large collection optic 134 and coupled back to theoptical platform 105. The light is reflected by a fold mirror 136 onplatform 105 and is detected by a sample signal detector 138.

A spectroscopy reference or gold coated wafer 128 is installed on anactuator arm 130. During a calibration process, this spectroscopyreference 128 is inserted into the output beam 140 to reflect the outputbeam 140 to the sample detector 138. This allows for the calibration ofthe sample detector 138.

FIG. 2 is a perspective view of the QCL spectroscopy system. It showsthe optical platform 105 with the combining optics including the foldmirror 120, dichroic mirror 122, and partially reflecting mirror 124.Also shown is the reference detector 126 and sample detector 138. Thecompact QCL tunable lasers 110A, 110B, 110C are installed on a lineunderneath the tuner electronics board 152. Also shown in the frontpanel 154 of the system 100 with the collection optics port 156, theoutput port 158 and a pointing laser 150 generates a visible spot thatcoincides with the non-visible emission through the output port 158.

FIG. 3 is a flow diagram illustrating one mode of operation for the QCLspectroscopy system 100 for non-interleaved spectral acquisition. Inthis operation, the QCL tunable lasers 110A, 110B, 110C are operated ina serial fashion.

In more detail, in step 180, the mirror or grating of one of the tunersis started to scan. This causes the emission or tunable signal of theQCL 110 to spectrally scan over its scan band. The electronics triggerthe laser pulse in step 182. Then the reference detector 126 measuresthe wavelength of the emission in step 184. The resulting data detectedby the sample detector are assigned to a wavelength depending on thewavelength detected by the reference detector 126 or based on theposition of the grating tuner 112.

In step 188, it is determined whether a full spectrum at the desiredsignal-to-noise ratio has been captured for the tuner. If not, then theprocess repeats. If adequate spectrum has been captured, the processrepeats for the next tuner in step 190. In this way, a spectrum isaccumulated for the scan band of each tuner until an entire spectrum hasbeen captured in step 192.

FIG. 4 is a flow diagram illustrating another mode of operation for theQCL spectrally spectroscopy system for interleaved spectral acquisition.

In this example, all of the grating tuners 112 of the QCLs 110 aretriggered to start scanning in step 200. Then, a trigger pulse is issuedto one of the tuners 110 in step 202. The reference detector 126determines the wavelength of the emission or the wavelength isdetermined by the position of the grating in the grating scanner 112.The signal detector 138 detects the response of the sample in step 204.The spectroscopy data are then assigned to the appropriate wavelengthbased on the response of the reference detector or the position of thegrating tuner in step 206. This process is repeated for the next tunerin step 208. In this way, each of the tuners detects the spectralresponse at a different point. In one specific example, the QCLs 110take turns generating a single pulse serially with this processrepeating until an entire spectrum has been acquired at the desiredsignal-to-noise ratio in step 210. Then the process completes in step212.

FIG. 5 is a detailed view showing one configuration for the externalcavity QCLs 110. In this example, the back facet light from the QCL 116is coupled via the external cavity lens 114 directly to the diffractiongrating of the grating tuner 112. The grating rotates around a rotationcenterpoint. This changes the light that is reflected back to the QCLchip 116.

FIG. 6 is a view of a grazing angle probe which is connected to the QCLspectroscopy system 100 in one embodiment.

In more detail, the grazing angle probe is coupled, via fiber opticcables 410 and 412, with a widely tunable QCL spectrometer 100. The IRlight generated from the QCL's 110 passes from the fiber optic cable 410through a plano-convex Ge lens 610 and is directed to the sample 132 bya mirror 612. A second mirror 614 then directs the light through asecond plano-convex Ge lens 616 to a return fiber optic cable 412, whichtransmits the light to the sample detector 138.

Resonant Scanning

Conventionally a laser can be tuned by rotating a grating, so that thefirst order of the grating is reflected into the external cavity. As themirrored grating is rotated, a different wavelength is selected that isreflected into the cavity and amplified. The constraints on a systemlike this include that the size of the assembly is dependent upon thesize, weight, and speed of the affiliated actuator that is utilized torotate it.

One embodiment avoids these constraints by keeping the grating fixed,but scans the laser beam across the grating utilizing a compact rotatingmirror. The advantages of this approach includes size, because themirror can be made very compact using conventional techniques and evensmaller with microelectromechanical system (MEMS) technology. The mirroris scanned across the grating very quickly. It accomplishes a fullwavelength scan in 1-10 milliseconds (msecs) or less, in oneimplementation, as opposed to the seconds required to move the muchbigger grating. The entire assembly is much simpler because themechanics and grating are decoupled and the mechanics to rotate the muchsmaller scanning mirror is not nearly as complex as what is required tomove the bigger grating. Furthermore, the range of motion required onthe mirror is half of what was needed for the grating.

The key elements of this system include a broadband QCL laser chipwithin an external cavity tuner that includes a high numerical aperture(NA) coupling lens that collimates the laser beam onto the mirror, whichthen scans the grating. The light is reflected back into thesemiconductor chip at a specific wavelength, which causes the laser tolaser at the desired wavelength. The laser light is then collimated bythe high NA output lens, which creates the output beam.

Approximately 11 degrees of motion are required to scan a sufficientdistance across the grating in order to reflect back light of 6 to 10micrometers.

FIG. 7 is a detailed view showing a configuration for the externalcavity QCL 110 using the resonant scanning system. This example uses astationary grating 296. Instead, a high speed scanning mirror 309 isused to couple light in the external cavity between the grating 296 andback into the QCL chip 116. In the preferred embodiment, the scanningmirror 309 is a resonant scanning mirror that is low mass and scans athigh speed. In this embodiment the relatively more massive grating 296is stationary and only the lightweight mirror 309 scans. As a result, itis possible to make a small, light scanning mirror 309 using MEMstechnology that is high speed such that a full wavelength scan ispossible in 1-10 msec if SNR is adequate. Also assembly is simplifiedsince scanning mechanics and grating are decoupled. Finally, the angularrange of motion for the mirror 309 is half of that for the grating inthe other configuration.

Resonant Scanner Spectral Sampling and Sorting

Because the time between laser pulses is long relative to the speed ofthe mirror 309, it is impractical for the mirror 309 and the pulses ofthe laser to be synchronized to provide a continuous sweep of thespectral range. Additionally, it would require a sophisticated timingsystem for the wavelength of any specific pulse to be pre-determined.

A more elegant approach is to pulse the laser, as the mirror moves. Thenthe position of the mirror 309 is determined using one or more of thefollowing: position feedback signal, the drive signal (the voltagesignal that is used to drive the mirror), or the clock signal (one roundtrip of the mirror is a single clock cycle). The position of the mirrorindicates which part of the grating 296 the beam is illuminating, whichis translated into an approximate wavelength via a lookup calibrationtable, for example. In another example, a reference detector system isused that resolves the instantaneous wavelength of the tunable signalfrom the tunable QCL system.

The spectral range is divided into a number of bins. The signal detectedfrom the sample for each of the laser pulses is placed in a bin, basedon its calculated wavelength. As the mirror continually scans and thelaser pulses, new wavelength measurements are taken. The pulsingcontinues until enough samples have been taken per bin to provide aspectrum of the measured sample. The resolution of this spectrum isbased on how many bins the range is divided into.

A side-effect from the sinusoidal motion of the mirror 309 is that thespectral distribution of the samples are grouped at the end of thespectral range.

FIG. 8 shows the electronics for the QCL spectroscopy system. In moredetail, one or more laser modules 110 with their respective resonantscanning mirrors 309 are used to generate the tunable signal 140 that itis spectrally scanned over the sample 132. The laser modules 110 aredriven by a pulse generator 810 through a laser driver 812. A drivesignal synthesis system 814 controls the resonant scanning mirrors 309of the QCLs 110. An automatic gain control circuit 816 is used foramplitude and to obtain the position output signal. This position outputsignal corresponds to the current position of the scanning mirror andthus directly corresponds to the wavelength of the tunable signal 140.The sample detector 138 is monitored by an analog to digital converter818. This provides digital data to a spectrum accumulation system 822.In more detail, the spectrum accumulation system 822 stores theinstantaneous response of the detector and the corresponding wavelengthas dictated by the position output signal. A clock reference 824synchronizes the pulse generator 810 and the drive synthesis system 814and triggers the acquisitions by the analog digital converter 818.

FIG. 9 is a plot of pulses as a function of wave number. The plot showsnumber of pulses per 0.2 cm−1 frequency bin for 1 sec total scan withpulse frequency of 200 kHz and scanner frequency equal to 110.0108 Hz.In one example, the minimum number of pulses in any bin=114. The scanamplitude is set to cover the range from 970 to 1190 cm−1. Spectrum issampled at different points on each scan until a spectrum isaccumulated. Generally, we want a maximum of about 1000 bins per tuner110.

FIG. 10 shows the electronics that enable the integrated pulse data tobe sorted into spectral bins. In the illustrated example, a 1000 binaccumulator functions as the spectrum accumulation unit 822. Each binaccumulates the response associated with a different range ofwavelengths within the scanband of the system 100. It stores theintegrated pulse signals from the A/D converter 818 in response to theclock signal from the frequency/clock reference circuit 824. The dataare stored into one of the bins based upon the sampled drive signal or aposition feedback signal for the resonant scanning mirror 309, whichindicate the instantaneous wavelength or wavenumber of the tunablesignal 140. In other embodiments, the bin is determined with respect tothe output of a reference detector that determines the spectrum of thesignal from the spectroscopy system.

Additionally, comparison of the position feedback signal with the drivesignal can be used to detect any anomalies in the motion (from shock andvibration, for example). A decision to ignore potentially bad data or tore-scan is preferably made based upon this information.

Processing

A laser pulse is triggered by the electronics at a specific wavelength.Then when the light is reflected back from the sample 132 to the sampledetector 138, the wavelength of light is correlated with the amplitudeof the signal on the detector. This process is repeated numerous timesto build up a full spectrum of absorption data. The key to thisprocessing allows the system to use a pulsed tunable laser to build upspectrum comparable to what one would get with an FTIR spectrometer.

One of the keys to pulse processing is the detector is sampled atdiscrete intervals, in order to avoid confusing background energy withthe reflected pulse energy. When the laser is dormant it is possible toobtain a baseline energy, so that the integrated pulse energy stands outfrom the background. The sum of the samples during a baseline region issubtracted from the sum of the samples during a pulse integration regionto give an integrated pulse energy for the pulse.

FIG. 11 illustrates the sampling of the sample detector 138 relative thepulse 1110 generated by the QCL tuners 110A-110C. The sample detector138 is sampled at discrete intervals such as 5 to 10 or more during eachpulse integration region 1110. The sample detector 138 is also sampledbefore and after the pulse region in order to get a baseline level 1112,1114. Sum of samples 1120 during baseline region is subtracted from sumof samples during pulse integration region 1110 to give integrated pulseenergy.

FIG. 12 illustrates an alternative to optical train design. In theoptical train illustrated in FIG. 1, the illumination beam from thetuners 110 is off axis with respect to the axis of the collection optics134. In contrast, FIG. 12 illustrates a collinear design. In moredetail, the tunable signal 140 from the tuners 110 is reflected by afold mirror 1210 to pass through the center of the collection optics 134to the sample 132. Light 141 returning from the sample 132 is thencollected by the collection optics 134 and coupled to the sampledetector 138 by a second fold mirror 1212.

Three main practical applications of the QCL spectroscopy system 100will now be presented. These applications can broadly be defined asusing the QCL spectroscopy system 100 for standoff detection, using theQCL spectroscopy system 100 with probes for near-range observation, andmicroscopy using the QCL spectroscopy system 100. All three of theseapplications demonstrate novel ways in which the QCL spectroscopy system100 provides significant improvements over existing technology.

Standoff Measurement with the QCL Spectroscopy System

FIG. 13 illustrates a portable embodiment of the QCL spectroscopy system100 allowing handheld remote inspections of surfaces at varyingdistances. In this embodiment, the QCL spectroscopy system 100 iscontained within a housing 1310 having a handle 1320 for greaterportability. With this configuration materials are analyzed on surfaces,and this measurement is usually made from several feet away from thesubject or sample (typically 3 to 5 feet) and up to very remotedistances, such as 100 feet. A red (visible) sighting laser 150 isincluded to help the user locate the correct sampling point, rememberingthat infrared laser radiation is not visible to the human eye. Uponprojection, the infrared sample beam 140 is set to 4 millimeters (mm) indiameter. The user does not have to worry about scattered radiation fromthe laser because the beam is eye-safe. The large IR collection optic156 provides efficient light collection from a remote sampling point132. Alternative embodiments of the system include a laboratory orientedconfiguration that enables the use of standard FTIR accessories. In thismode of operation, standard IR cells, reflectance accessories, and evenmicroscope accessories can be accommodated.

The portable embodiment of the QCL spectroscopy system 100 describedabove allows handheld remote inspection of surfaces at varyingdistances. In order to enable this mode of operation the co-linearoptical arrangement shown in FIG. 12 is used where the laserillumination path 140 follows directionally the same effective path asthe returning reflected beam 141. This allows the instrument to be usedfrom distances of a few inches to several feet from the sample surface,making it ideal as an inspection tool or as a stealth or non-contacttool for the detection of materials on surfaces for law enforcement orsecurity applications. Applications in this mode of operation arefeatured below.

Stand-Off Applications of the Tunable QCL Spectrometer

Fundamentally, a broadly tunable QCL spectrometer 100 functions as anyother infrared spectrometer. It may be used in a laboratory environmentfor standard transmission measurements on solids, liquids and gases. Thelaser also inherently provides a high optical throughput, for tracemonitoring applications, as well as for low level transmission or lowreflectivity measurements, as experienced with highly absorbing samplesubstrates, or with micro-sampling methods.

One attribute utilized in a stand-off arrangement is the higher spectralpower density (at a particular wavelength) at the sample; estimated tobe one or two orders of magnitude greater, at a particular wavelength intime, than a traditional IR source as used in an FTIR. This increasedperformance is realized in terms of higher SNR (signal-to-noise ratio)for energy returning from remote surfaces. An added benefit for thisapplication is the directional characteristics of the IR beam thatresults from physical characteristics of the laser source (beamcoherence with a minimally divergent beam). This feature enables samplesto be accurately targeted, and the minimum beam divergence ensuresoptimal coupling between the infrared beam and the remote sample.

The QCL spectrometer 100 is particularly useful in the area of remote orstand-off measurements. This mode of measurement is unique for routinesampling and is usually impractical with a conventional FTIR-basedsystem. Reflectance measurements from surface with a conventional FTIRrequire a very close-coupled reflectance accessory where the distancesare kept very small between the sample and the incoming focused samplebeam, and where equally closely coupled collection optics are requiredto direct the beam efficiently back to the instrument's detector. Thisincludes both specular and diffuse reflectance measurements. In bothcases, the need to focus the beam on to the sample, and the need tocollect a rapidly diverging beam (specular measurement) or a highlyscattered beam (from a diffuse surface) limits the illumination andcollection geometries to about a centimeter, at the very most. At largerdistances, the ability to optimize the coupling of the focused beam islost, and there is too much divergence or even scattering from theemergent beam to enable efficient light collection without the need of avery large optical system.

There are commercial instruments (FTIR and Raman) for handheld stand-offmeasurements and non-contact measurements of samples. These are limitedto close-up measurements, where the spectrometer is used a fewmillimeters from the surface or for attenuation total reflection (ATR)based measurements where actual surface contact is required. While bothof these approaches work, they have limitations, both in terms of basicperformance, and in the case of ATR, where there is a high risk ofcontamination of the sampling head, and/or the sample surface. Astand-off measurement eliminates these problems and risks. QCL can beused for a complete remote stand-off measurement where accurate spectraldata are acquired for materials on surfaces without the safety and/orcontamination issues highlighted above.

While there are handheld FTIR spectrometers for the non-contact,remote/stand-off measurement of surfaces and for the characterization ofmaterials on surfaces, these devices are constrained by distance fromthe subject. Typical stand-off distances for such measurements with anFTIR are a few millimeters to a centimeter or two (for a reflectivesurface) at best. Even in the laboratory, with a bench-top FTIR,reflectance measurements with standard accessories only allow aseparation from the sample surface of about a centimeter or two. Thedirectional properties of the laser, plus the higher spectral powerdensity enable good quality spectra, comparable to laboratory qualityFTIR spectra, to be obtained from surfaces at distances of one foot tosix feet away from the subject, and up to 100 feet for truly remoteapplications. This opens up a range of new applications, not possible byFTIR, which include remote detection of explosives and chemical agentson surfaces (military and public safety), surface contaminationmeasurements, and the determination of surface composition ofnon-accessible surfaces, which can include surfaces inside vessels orcontainers, surfaces in dangerous environments, and measurements fromhot (high temperature) surfaces. The latter is an importantconsideration for process monitoring and catalyst surface studyapplications.

Stand-Off Measurement of Chemical Agents

As indicated, one area in which the QCL spectroscopy system 100 isparticularly useful is in the stand-off measurement of chemical agents.Chemical agents can be measured whether present as a residue or thinfilms on a surface or in a pool of liquid.

When known chemical agents are present as a thin film or residue on areflective surface, such as an aluminum surface, spectral data obtainedby stand-off measurement with the QCL spectroscopy system 100 show acombination of reflection and transmission like spectra, resulting inmixed mode measurements for some samples. In spite of the mixed modeeffects, the spectra are still unique and can be used, via comparativemethods, to identify the agents.

A method for using the QCL spectroscopy system 100 to remotely measurecontaminated reflective surfaces is useful in instances such as inmilitary or public safety substance detection where the subject, with apainted metal surface, has residues of a common explosive. When spectraare compared for painted surfaces where one set of samples arelaboratory prepared references recorded on a laboratory FTIR with theaid of a 30° angle of incidence reflectance accessory, and the other setcontain explosive residues on the surfaces, measured by the QCL at adistance of about 5 feet, the spectra measured by the QCL will exhibitunique anomalous dispersion effects as typically observed in thin filmreflectance spectra from highly absorbing substrate surfaces. From thepoint of view of characterization, these materials can bedifferentiated, even though they may be convolved with some of thespectral characteristics of the background or substrate. This format ofspectrum can be used directly with a library of similarly recorded datafor known substrate materials. If there is a requirement to compare therecorded spectrum with a standard library of spectra in transmittance orabsorbance format, then the spectrum may be qualitatively compared tothe library after a band inversion (for the transmittance format).

The traditional infrared measurement of liquid samples was by lighttransmission through the sample. Samples were measured as a liquid filmbetween IR transparent windows. The stand-off measurement of chemicalsin liquid form is more complex because the liquid has both transmissiveand reflective properties. The stand-off analysis of liquids on surfacesrequires the measurement of the IR light reflected either through or offthe surface of the liquid.

If the liquid forms a thin film on the surface, such that the lightpasses through the liquid and is reflected back from the surface and thereflected light is measured, then a “transmission” spectrum is recorded.This mode requires that that the surface is reflective, such as analuminum surface.

Reflection from an infrared absorbing surface, such as the liquid, is acomplex function and is related to the refractive index of the material.The resultant specular reflective index spectrum correlates to changesin refractive index and provides a very different, derivative likespectrum.

If the light partially transmits through the liquid (in areas where thesample has low absorption/high transmission) and also reflects from thesurface of the liquids, then the result is known as a mixed modespectrum: partially transmission-like partially specular(refractive-index).

In a method for using the QCL spectroscopy system 100 to remotely recordthe spectrum from a pool of liquid or a liquid smeared or spilled on asurface, the QCL spectroscopy system 100 is used in a remote stand-offarrangement, to measured spills on a linoleum surface at a distance ofabout 3 feet. The obtained spectra will compare well with those recordedin the laboratory. The generated absorbance form of the spectra isdirectly compared to the laboratory reference spectra forcharacterization and identification. This is a good example where anunknown spill is observed, such as a potential HAZMAT spill, and thematerial can be safely identified from a distance. This is in contrastto existing FTIR and Raman handheld instruments that require the user tobe in a HAZMAT suit and be in extremely close proximity to the hazardousmaterial.

Here also, materials deposited as thick films, designated “infinitelythick” relative to the IR absorption, will yield characteristicallydistorted specular reflectance spectra. Numerical conversions such asthe KK-transform (Kramers-Kroenig Transformation) are applied toreformat the data into an absorption-style of format, by separating therefractive index components from the spectra.

For both residues or thin films and for liquids on surfaces, the spectraobtained by stand-off measurement with the QCL spectroscopy system 100are reproducible and can be correlated to standard reference spectrawhen available. The spectra have anticipated “distorted” appearancesthat are understood and are a function of the nature of the sample andthe sample film thickness. These reflection/refractive index effectsfrom the thicker films are reproducible and are equally characteristicof the sample spectrum as the normal transmission spectrum. The chemicalagents can be both characterized and identified from the stand-offspectra by building a custom data base that features transmission,mix-mode and specular (refractive index) spectral data. The KK transformis preferably applied to examples where the spectral data is mostlyspecular rather than mix-mode.

Stand-off measurements are important for a wide range of practicalapplications, for example; surface quality or contamination measurementsfor engineering and production applications, security applications,where dangerous materials such as chemical agents and/or explosivesmight be involved, and for law enforcement, such as for illicit drugdetection (both production and usage). Unlike other methods, this can beperformed at a reasonable distance, and without contamination of eitherthe surface or the instrument.

Chemical Imaging of Large Surfaces

An embodiment of the current invention is drawn to a method for usingthe QCL 110 together with an IR array (microbolometer or MCT) to providea 2D “chemical image” of the surface. This arrangement is illustrated inFIG. 14. It comprises the QCL laser 100 that images a sample 132. Animage of the sample 132 is then detected by an infrared camera 1410 thatcomprises a two dimensional detector array such as a 100 by 100 elementmicrobolometer array. This allows scanning a surface to detect thepresence of Explosives, chemical warfare agents (CWAs), toxic industrialchemicals (TICs), and non-traditional agents.

Applications include:

a. Validating that military or emergency response vehicle has beendecontaminated.

b. Validating that a large area, such as a warehouse, office building,etc. are decontaminated.

c. Scanning the trunk/door handles or tires of vehicles as they enterparking lots, underground garages, or other areas.

d. For detection of explosive residues to avoid car bombs at large crowdgathering events.

The QCL laser 110 in combination with the IR array 1410 could be tripodmounted for large surfaces, of a vehicle, for example, or portable forthe trunk/door handles.

When used for large Area Scanning, each 1.5′×1.5′ section is imaged at100×100 resolution (4.6 min spatial resolution) of the bolometer.Surface concentrations of 10 g/m² or less are preferably detected. When24″ optics are used, the total area to be interrogated is 800 sq. ft.Scanning can be completed in 11 minutes.

Smaller, targeted area scanning (e.g. Car Trunk Handle) enables:

a. Portable equipment

b. Rapid scanning in seconds

c. Trace-level concentration detection

d. Low-cost device

Detection of Scattered Contamination on Surfaces

One embodiment is drawn to a method and system for detecting scatteredcontamination patterns on surfaces using the QCL spectroscopy system100. As shown in FIG. 15, the QCL-based device 100 is mounted under ornext to a vehicle and shines the emission from the laser module(s) 110on the ground or vehicle 1510 for detection of scattered contamination.The detector 138 is separated from the QCL modules 110 to detect thediffuse reflectance spectrum. Such contamination patterns might betypical of a situation when an explosive disperses the chemical threat(e.g. CWAs/TICs/ NTAs) over a large area and typically there aredroplets 1512 scattered on the surface 1510.

The QCL spectroscopy system 100 scans the surface randomly and collectsspectra, which after certain averaging show that a threatening substanceis present.

In other embodiments, high speed QCL scanners (such as the ResonantScanner) would enable such measurements.

In other embodiments, the QCL spectroscopy system 100 is also mounted onrobots or unmanned aerial vehicles for similar operation.

Protection of Large Facilities

An embodiment of the current invention is drawn to a system fordetecting chemicals at long-range distances using the QCL spectroscopysystem 100. The QCL spectroscopy system 100 is placed at a selectedlocation 1610 within a room 1612, such as an airport terminal. Thesystem 100 scans across a long distance by transmitting beams 140 acrossthe room 1612. Properly placed retroreflectors 1614 are used to generatea return beam 141 back to the system cover the area to be protected.This arrangement is illustrated in FIG. 16.

The retroreflectors 1614 provide essentially an “optical path” fordetection of any chemical threats, such as gases or vapors fromexplosives, CWAs, TICs, or NTAs. In one embodiment, multipleretroreflectors 1614 are used, being located in different corners of theroom 1612. The beam 140 from the system 100 is either divided into threebeams or successively transmitted to each of the retroreflectors 1614,depending on the embodiment.

The eye-safe lasers can be used in areas with large crowds of people,both indoors and outdoors. Fast readings allow for quick detection andimmediate warning alerts. 24/7 coverage can be provided with the laserbouncing off the retroreflectors 1614 in a preset timing pattern.

The use of the QCL spectroscopy system 100 in the current arrangementwith low-cost, optimally placed retroreflectors 1614 provides real-timelarge area protection and high sensitivity line of sight detection.

Combined Gas and Standoff Detection in Single Device

An embodiment concerns a system for detecting chemicals at a stand-offdistance and detecting gas using the QCL spectroscopy system 100. Thissystem allows users to detect both harmful vapors and surfacecontaminants with a single device.

The system has a projected gas detection limit: SF₆: 8 ppt, Sarin: 70ppt, Mustard: 237 ppt (5-10 m path).

Advantages of the system include a reduced false alarm rate whencompared to IMS (high resolution IR spectroscopy) and the ability todetect a higher number of compounds, including CWAs, NTAs, precursors,impurities, binders, etc. relative to the use of Far IR spectroscopy.

Detection of Chemicals on Shoes

One embodiment is drawn to a system for detecting chemicals on shoesusing the QCL spectroscopy system 100. This system is illustrated inFIGS. 17A and 17B. A QCL-based device including the QCL spectroscopysystem 100 is used to detect particles that come off of passengers'shoes as they walk through check points, such as airports, events, etc.

In this embodiment, the QCL spectroscopy system 100 is housed in anenclosure 1710. The enclosure 1710 has shoe-sized openings 1720, orstep-in ports. When the passenger steps into the step-in ports 1720,their shoes 1722 are puffed with air 1724. A vacuum is then used tosuction any released particles onto a silver membrane filter throughsuction ports 1724. The QCL beam then identifies any chemicals trappedin the filter. Additional embodiments of the invention further comprisemagnetometer technology, allowing the identification of explosives inaddition to chemicals.

This simple, walk-in concept could greatly contribute to public securityby supplementing other, pre-existing safety measures. Scanning is donewhile other screening is taking place. Sampling time totals only 3-4seconds and processing time is less than 9 seconds. With a smallfootprint, at 1×2×3 feet, the detector fits within other systems, suchas metal detectors. No additional training of airline or public safetypersonnel would be required.

Stand-Off Detection of Disturbed Earth Using QCLs

Detection of disturbed soil is of particular importance on thebattlefield as it can indicate the emplacement of an improvisedexplosive device (IED), trip wire or pressure plate. When soil is firstdisturbed the quartz, found in most soils, is coated with otherminerals. As the soil is weathered, the quartz is more exposed, whichgives a stronger signature—the Reststrahlen Contrast—particularly in the8-10 μm (1,250−1,000 wavenumbers) range. So the spectral pattern betweendisturbed soil and non-disturbed soil is different and recognizable.This effect is particularly important in Afghanistan where much of thesoil is sand, with high quartz content, and monochromatic, often makingdetection of disturbed earth by visual techniques difficult. However, aswith most sensor systems, this is not a 100% solution as these spectraldifferences cannot be discerned during rain, after snow cover or afterdust storms.

Spectral analysis research to date has been done with laboratory FourierTransform Infrared Spectrometers (FTIR), which are slow, require contactwith the soil and are not very practical for use in the field. A fast,standoff device is needed to quickly detect the same IR signaturechanges.

In a method for using the QCL spectroscopy system 100 as a standoffsensor to detect patterns of disturbed earth, the QCL spectroscopysystem 100 has a much higher sensitivity than FTIRs thereby enablingstandoff detection. The QCL spectroscopy system 100 has been shown tosuccessfully detect the reststrahlen signature.

An additional embodiment of the current invention is the optimization ofthe portable QCL spectrometer system shown in FIG. 13 for detectingdisturbed earth in desert environments. The modified QCL spectroscopysystem 100 is lightweight and has low power requirements, enabling it tobe carried by dismounted troops or mounted on a variety of vehicles.Furthermore, it preferably includes a rechargeable battery or operatesfrom vehicle power. Power consumption is preferably 30 Watts or less.Operational time on one battery charge preferably ranges from 4-6 hrs at20% duty cycle. It can tolerate 0-140° F. temperatures, 10-95% humidity,operate at 0-5000 feet above sea level. It is inherently rugged due toits use of solid state components. It can operate either in the daytimeor the nighttime. In embodiments, it is further outfitted with GPS,video, RF links and the common sensor interface protocols. It is eyesafe. A further embodiment of the current invention is this portable QCLspectroscopy system 100 modified to contain only one laser module. Thereis great potential for size and complexity reduction because in someexamples it is possible to detect the reststrahlen band using only onelaser module (versus the three laser modules used in the current QCLspectroscopy system 100 to detect explosives and chemical agents). Usingonly one module would reduce the cost, size and weight of the laserengine by over 50%.

FIG. 18 is a flow diagram illustrating the method of detecting disturbedearth using the QCL spectroscopy system 100. In step 1810, the QCLspectroscopy system 100 is aimed at the soil. Most of the time, the QCLspectroscopy system 100 detects the signature of undisturbed soil instep 1820 and uses this data to establish a baseline measurement in step1830. If no changes are detected from baseline, the spectrometercontinues detecting the baseline measurement and notes no changes, asseen in step 1860. When the signature changes, the QCL spectroscopysystem 100 automatically detects the change in step 1840 and warrantsfurther investigation as seen in step 1850. Guided by the operator, orpotentially with an automatic scanning device, the QCL spectrometersystem 100 then interrogates adjacent parcels of soil so as to establishthe boundary enclosing the disturbed earth.

The portable QCL spectrometer system used in the current method furtherincludes built in marking devices, such as spray paint, or video feedsthat are used to record the location and communicate it back to anoperator. GPS or RF modules are also preferably incorporated. At thispoint other confirmation techniques are also used in some examples toconfirm the emplacement of an IED, trip wire or pressure plate andestablished routines are used to disrupt/disable the IED.

One embodiment of the current invention is the method for detectingdisturbed earth using the QCL spectroscopy system 100 mentioned abovefurther comprising a ground penetrating radar (GPR) system such as theVISOR 2500 NIITEK Husky Mounted system to enhance detection performancethrough a dual sensor system. To cover a large area (e.g. a whole road)the laser is located in a central enclosure in front of the vehicle. Ascanner and optical collection system direct the laser beam towardsdifferent spots on the ground to increase the interrogation area. Theinterrogation area is a single 5-10 mm pixel or, for example, a 3×3 sqin area imaged with a 2D multi-pixel array. The array offers a widerground coverage but the sensitivity of the measurements would bereduced. A line imager could also be used. A further embodiment of thecurrent invention is drawn to method for detecting disturbed earth usingthe QCL spectroscopy system 100 in combination with NIITEK mentionedabove wherein miniaturized versions of NITEK and the QCL spectroscopysystem 100 are integrated into UGVs.

Another method is used for detecting disturbed earth using the QCLspectroscopy system 100 mentioned above, wherein the spectrometer isutilized in a handheld or binocular configuration by soldiers on foot,who are scanning the ground 10-20 ft ahead of them. Dismounted troopsoften work off road and in narrow pathways, choke points or mountainpasses that cannot accommodate sensors mounted on ground or aerialvehicles. In a further aspect of this embodiment, this method detectingdisturbed earth using the QCL spectroscopy system 100 in a handheld orbinocular configuration is used to search for trip wires. Walkingparallel to, but at a safe distance from a road, the soldier finds earthdisturbed when trip wires are buried. Special audio or visual warningsinstantaneously alarm the soldier as the disturbed area is approached.This sensor is potentially miniaturized so that it is mounted on thehelmet of dismounted soldiers, offering convenient “hands-free”, realtime disturbed earth detection.

A further embodiment is drawn to a method for detecting disturbed earthusing the QCL spectroscopy system 100 mentioned above in which the QCLspectrometer 100 is integrated with an interrogation arm. The QCLspectroscopy system 100 is mounted on the IED Interrogation Armdeveloped by Night Vision and Electronic Sensors Directorate tosupplement existing sensor modalities (video and metal detectors).

The method for detecting disturbed earth using the QCL spectroscopysystem 100 described above is modified so that the QCL spectrometer 100is integrated into unmanned aerial vehicles (UAVs). Because of its lowweight, the portable QCL spectroscopy system 100 shown in FIG. 13 ismounted on a small payload UAV that hovers only a few meters above theground. Alternatively, a QCL spectroscopy system 100 with largercollection optics and more powerful lasers, although slightly heavier,could potentially detect disturbed earth from a UAV several meters abovethe ground.

FIG. 19 shows data collected using the commercial portable QCLspectroscopy system 100 shown in FIG. 13 on standard soil around theMassachusetts countryside. The curves of disturbed/undisturbed earthdeviate from each other in the 8-10 μm range and then approach eachother around 7.5 μm. The portable QCL spectroscopy system 100 shown inFIG. 13 was held at approximately 6 inches off the ground and themeasurements were acquired in a few seconds. The 6 inch distance wasused because the current commercial portable QCL spectrometer unit wasdesigned and optimized for this distance. Other designs would increasethe standoff distance. To simulate a “looking ahead” arrangement, underwhich a dismounted soldier or vehicle are looking ahead of them at adistance, the QCL spectroscopy system 100 was also used to test theeffect of angle on the measurements. Assuming the QCL spectroscopysystem 100 is held 3-4 ft above the ground and looking ahead at ground10 ft away, the QCL spectrometer beam will intersect the ground atapproximately a 60° angle from normal perpendicular. FIG. 19 shows theresults of measurements at angles varying between 0 and 60°, indicatingthat the reststrahlen effect remains very strong even at steep angles.Using a slightly larger 6″ lens and with the sensitivity enhancements,we predict that a handheld QCL spectroscopy system 100 could detectdisturbed earth at 10 feet away. As mentioned above if only one laserwere used, the device could shrink to flashlight size and ultimately behelmet mounted.

A further embodiment of the method for detecting disturbed earth usingthe QCL spectroscopy system 100 mentioned above comprises usingDifferential Spectroscopy (DS) algorithms. The use of DS algorithms is atechnique used by spectroscopists to detect “anomalies” in a datastream. DS compares one measurement to the next one over time andidentifies changes attributed to a change in the target properties. DSis typically not used with FTIRs because they are too slow and requirecontact with the sample. The QCL spectroscopy system 100 has beendeveloped as a high speed device and acquires near instantaneousspectral information from the ground. As part of the DS algorithm,algorithmic techniques ranging from Peak Finding and Match Filtermethods, to First/Second Derivatives techniques and other more involvedmathematical tools are incorporated. These allow the detection of thetelltale spectral change in a wide variety of soil types andenvironmental conditions and to measure changes over time.

When the QCL spectroscopy system 100 is used by dismounted soldiers,special provisions are included. For example, when a soldier is stressed(e.g., under assault) the QCL spectroscopy system 100 might accidentallybe pointed at the sky or objects other than the ground (such as abuilding, another soldier), so the algorithm needs to know when it isseeing ground. To accomplish this low cost MEMS accelerometers andgyroscopes (used in many consumer products) are incorporated todetermine whether the QCL spectroscopy system 100 is properly pointedwithin a preselected cone of, say, 50-70° degrees off normalperpendicular, and appropriately process or ignore the data (or signalthe soldier) depending on the reading.

The method for detecting disturbed earth using the QCL spectroscopysystem 100 mentioned above further includes using thermal sensors(FLIRs) to detect disturbed earth. A QCL spectroscopy system 100incorporating a FLIR constitutes a good dual sensor approach.

A further embodiment of the current invention is drawn to a method fordetecting disturbed earth using the QCL spectroscopy system 100mentioned above in which the QCL spectroscopy system 100 has enlargedcollection optics 134. After the laser beam is bounced off the earth,the size of the collection optics determines how many photons arefocused on the IR detector 138. More photons enhance sensitivity. FIG.20A illustrates a QCL Cassegrain optical system. Cassegrain mirrors arelighter than lenses; therefore, collection systems as large as two feetin diameter can be practically developed and deployed.

Using extensive data from various backgrounds, substrates, substances,and distances, the performance of the QCL spectroscopy system 100 undervarious conditions and configurations can be predicted. FIG. 20B showsthe effect of larger collection optics on the standoff distance fordetection of disturbed earth. Standoff distances of approximately 20 mor 45 m (˜65 or 150 ft) can be achieved with, respectively, 1 and 2 footcollection optics, producing a measurement in one second.

A further embodiment of the method for detecting disturbed earthmentioned above includes using a QCL spectroscopy system 100 modified tohave an increased duty cycle. The QCL spectroscopy system 100 operatesat 200,000 pulses per second, but there is still quite a bit of “silent”time between pulses resulting in a duty cycle of only about 2%. A lowduty cycle allows for laser cooling and temperature stabilizationbetween pulses. However, QCL spectrometer systems can be used in whichthe duty cycle is increased to 10%, i.e. by as high as a factor of 5,which would increase sensitivity by a similar factor.

The method is further modified to include the use of a QCL spectroscopysystem 100 with a higher sensitivity detector. The QCL spectroscopysystem 100 uses a TE-cooled Mercury Cadmium Telluride (MCT) detector138, in the current embodiment. However, QCL spectrometer systems can beused with higher sensitivity detectors, such as immersed TE cooledMercury cadmium telluride (MCT) that works well for disturbed earthdetection and would be 10 times more sensitive.

A further embodiment of the method for detecting disturbed earthincludes using a QCL spectroscopy system 100 with increased laser power.Higher currents are used to increase the power per laser pulse by afactor of 3-5.

Stand-Off Applications in Pharmaceutical Environments

In addition to the military and public safety applications describedabove, the QCL spectroscopy system 100 has many uses in the laboratoryor pharmaceutical environment. When used in a standoff arrangement, theQCL spectroscopy system 100 is a new and useful tool for both assessingcontamination in pharmaceutical environments and for bacterialidentification. Both of these applications will be described in furtherdetail below.

Reaction Vessel Contamination Monitoring

The conventional process for monitoring contamination in reactionvessels involves taking several swabs in pre-identified “hot spots” of a10×10 cm area within a reaction vessel to verify cleanliness. Methanolis used to remove the potential contaminants from the swab and then HPLCor TOC is used to detect contamination. The threshold level ofcontamination is typically approximately 1 ug/cm2. Although there aresome active ingredients that need to be as low as 0.015 ug/cm2, the vastmajority are above 0.6 ug/cm2. Perhaps 50% are above 1 ug/cm2.

The Food and Drug Administration (FDA) requires three successfulcleaning runs, where the cleanliness of the vessel is verified aftereach run in order to validate the cleaning methodology. After thisvalidation there is no need to test for cleanliness between switch over,as long as the validated cleaning method is used. The problem is thatthis is not a very empirical method—how hard or thoroughly did you swabthe area. Also, it is time consuming because it takes a several minutesat least to get results. Ideally, a user would like to go to cleaningmonitoring after each switch over. Through cleaning monitoring they willbe able to clean the vessel until the contaminants are down toacceptable levels, rather than cleaning until they reach the validatedstandard (which might require overcleaning the vessel and usingexcessive water and time). There are various other alternativetechniques, but they each have problems:

Raman is not sufficiently sensitive in its handheld embodiment.

UV spectroscopy has a hard time working with the surfaces.

One embodiment of the current invention is drawn to a method fordetecting contaminants on pharmaceutical surfaces using the QCLspectroscopy system 100. In the preferred embodiment, the QCLspectrometer 100 described previously is used in a standoff arrangement,such as 0.15 to 0.3 meters from the inner wall of the reaction vessel,to analyze the inner reflective surfaces of the reaction vessel.Preferably the device is deployed in a standoff mode or combined with agrazing angle probe coupled to it by a fiber. By taking high sensitivitymeasurements at a standoff it becomes a practical device for doingcontamination monitoring.

FIG. 21 is a flow diagram illustrating the method of detectingcontaminants on pharmaceutical surfaces.

In step 2110, the QCL spectroscopy system 100 is positioned towards apharmaceutical surface at a stand-off distance. The IR spectra are thenmeasured by QCL spectroscopy system 100 in step 2120. The IR spectra arecompared to a standard of known levels of contamination in step 2130 andin step 2140 the amount of contamination present is determined. Thelevel of contamination is compared to a previously determined thresholdlevel of acceptable contamination in step 2150. If the contamination isbelow this level, then the cleanliness is validated in step 2160. If itis not below this level, then the surface must be cleaned further instep 2170 and the cleaning validation must be repeated.

In an alternative embodiment, the spectra of the pharmaceutical surfacecan be measured using the QCL spectroscopy system 100 fiber opticallycoupled to the grazing angle probe shown in FIG. 6. The use of fiberoptic probes is discussed further below.

QCL-Based Detection of Bacteria

Bacteria that are confined in a vial and given nutrients emit certaincharacteristic gases based on the type of bacteria in the vial and basedon the nutrients they are given. These gases rise into the head space ofthe vial. Measurements are taken across the vial using the QCL laserbased absorption spectroscopy system 100. These measurements have beentaken previously with an FTIR, but with a QCL there is more energy perwavelength, which results in faster measurements and measurements withlower detection levels.

FIG. 22 is a flow diagram illustrating the method of identifyingbacteria using QCL spectroscopy system 100.

In step 2210, an appropriate growth media is selected. Different typesof growth media will cause the bacteria to produce different gaseousproducts. In step 2220, a pure culture of bacteria is grown in the mediain a sealed vial, allowing any gasses produced during the growth of thebacteria to accumulate. In step 2230, the IR spectra of the gaseousheadspace of the vial are measured using the QCL spectroscopy system100. In step 2240, the spectral data obtained are used to identify thegasses present. The gaseous composition is then evaluated in step 2250.It is possible that the gasses produced are consistent with the presenceof a single type of bacteria, in which case, the bacteria has beenidentified in step 2260. Alternatively, it is possible that theinformation gained from the gaseous composition has narrowed the fieldto a few possible types of bacteria. In this instance, repeating thetesting process with a different type of growth media may allow forbacterial identification.

Near-Range Use of the QCL Spectrometer System with Fiber Optic Probes

The use of the QCL spectroscopy system 100 with fiber optic probes fornear range or direct observation of targets is a significant improvementover previous technology. In the past, when coupling an IR spectroscopysystem to a fiber optic probe, such as an attenuated total reflectance(ATR) probe, FTIR was used. As will be described in more detail below,when using FTIR with an ATR probe, the return signal is very weakrequiring the use of a high sensitivity detector. When coupled to afiber optic probe, the QCL spectroscopy system 100 produces a strongersignal, resulting in higher sensitivity and faster measurements.Described below are several different systems and methods for using theQCL spectroscopy system 100 with fiber optic probes that representsignificant improvements over prior FTIR-based technology.

Monitoring of Chemical or Biological Reactions with QCL SpectroscopySystem 100

Typically, reaction monitoring is done in the mid-IR with a combinationof an FTIR coupled to either a fiber, which is then connected to an ATRprobe or a light guide connected to an ATR probe. The light source of anFTIR is a conventional globar, which is a large source that is difficultto couple to a fiber or light guide with high efficiency. Because ofthis, only a small percentage of the light from the globar is coupledinto the fiber or light guide. Therefore, the return signal is veryweak, which requires a very sensitive detector, such as a liquidnitrogen cooled detector, in order to detect the return signal.Furthermore, the sensitivity of the FTIR based reaction monitoring islimited by the amount of light that is successfully coupled and thenreturned to the FTIR's detector.

To compensate for high loss (such as through long lightpipes or smalldiameter fibers), FTIRs typically use high sensitivity, liquid nitrogencooled detectors. These detectors are inconvenient because theyconstantly need to be recharged. In addition, an FTIR is extremelyvibration sensitive because at its heart it is an interferometer.

In the case of using a QCL spectrometer, the laser is more efficientlycoupled into the fiber than the FTIR globar source and the power levelper wavelength is also higher. This high coupling efficiency is becauseof the high spectral radiance of the laser based system relative to anFTIR globar source (six orders of magnitude higher). Therefore, thereturn signal through the reaction monitoring probe is significantlyhigher than for an FTIR. This results in higher sensitivity, fastermeasurements, and not requiring the use of a liquid nitrogen cooleddetector.

In the preferred embodiment, a chemical or biological reaction ismeasured by a QCL spectrometer 100 described previously opticallycoupled to a reaction vessel in or substrate on which the reaction istaking place in process material. The optical coupling is preferablyachieved with optical fiber that extends between the spectrometer andthe probe such as an ATR probe. A detector is used to detect the lightreturning from the process material. A controller determines thespectral response of the process material, which is used to assess theprogress of the chemical or biological reaction. Preferably, thisspectral response is then used by the controller to control the reactionparameters such as time and temperature and other variables that affectthe progress of the reaction.

FIG. 23 is a flow diagram illustrating the method of monitoring achemical or biological reaction with an ATR probe connected to the QCLspectroscopy system 100.

In step 2310, the ATR probe coupled to the QCL spectrometer 100 isplaced in contact with a chemical or biological reaction. In step 2320,the IR spectra of the substrate are then recorded by the Quantum CascadeLaser based analysis system 100 at various time points as the reactionproceeds. In step 2330, the spectra obtained are compared to a standard.The rate of the reaction is determined based on this data in step 2340.In step 2350, the reaction parameters may be modified to regulate therate of the reaction and the reaction rate may be determined.

QCL Spectrometer with ATR Probe for Cancer Detection

The benefits of the QCL attenuated total reflectance (ATR) system versuscurrent cancer detection methodologies are as follows:

1. increased accuracy of detection,

2. operation by relatively low skilled personnel, minimal trainingrequired,

3. extremely portable system that can be used in rural areas or indeveloping countries that do not have access to pathology labs, and

4. a point of care detection system that can be used in clinics anddoctor's offices for low cost and more extensive screening of cancer.

Referring to FIG. 24, infrared technology, with the performance benefitsof the QCL, can provide another, different level of diagnostics that islinked to in situ and in vivo measurements. This approach is not microimaging, but instead is a chemically sensitive probe 310 that is used atthe time of an examination and/or an operation on patient 312 to providethe examiner with an instant diagnosis of suspect tissue as shown inFIG. 24. One issue has been the presence of water and/or mucous on thesurface of the tissue. ATR probes can be used for the examination ofmaterials in an aquatic environment.

The QCL spectrometer 100 that was mentioned earlier is modified for usewith the ATR approach. The benefits offered are similar to those citedearlier, i.e. performance, size and cost, but with the added capabilityto provide in vivo measurements. The ability to combine the opticalthroughput characteristics of the QCL system with infrared opticalfibers opens up the possibility to provide the examiner with apoint-of-care, in vivo, diagnostic tool. For example, this tool is used,in one implementation, by hygienists to look for potential mouth cancersduring routine checkups, as shown in the figure. In addition it can beincorporated into colonoscopy probes to detect flat cancerous areas inthe colon that are often difficult to detect using conventional visualtechniques. Another application is during cancer surgery to determinewhether all the cancerous cells have been removed.

In the preferred embodiment, the QCL module 100 is combined withspecially designed fiber optic probes into a portable and easy-to-useATR cancer detection system.

The system provides a clinically-usable diagnostic infrared probespectrometer system that reliably discriminates between cancerous andnon-cancerous lesions in biopsied and fixed tissue examined in vitro orin vivo as shown.

FIG. 25 shows Attenuated Total Reflection (ATR) probe 310 and theassociated Quantum Cascade Laser (QCL) based analysis system 100.

ATR requires the specially designed optic probe 310 to be made from ahigh index of refraction optical material. This sampling technique hasbeen applied in infrared spectroscopy for many years. Its use formedical applications began in the 1970s for the study of skin cancer.Since that time it has been used for both the study of normal, healthyskin tissue and also diseased tissue. ATR probes have demonstratedsuccess in examining cancerous tissue that is at or near the surface ofthe body. The oral cavity is one such area; the cervix and colon areothers. Work has already been reported on in situ diagnostics forcolorectal cancer patients using an ATR probe. Traditionally, moststudies have used an ATR probe on FTIR instrumentation which narrowrange limits its applicability. QCLs address this limitation.

In a preferred embodiment, an ATR probe coupled, via optical-fiberumbilical 314, with a widely tunable QCL spectrometer 100, as describedpreviously, covering the spectral range 6 μm to 12 μm, which is the samerange typically used with FTIR/ATR systems. This measurement rangecovers the essential spectral area for infrared cancer studies.Importantly, the QCL spectrometer 100 provides two orders of magnitudegreater sensitivity versus an FTIR.

An ATR system includes an Internal Reflective Element (IRE) 316 that isused to probe the tissue, fiber optics 314 transmit IR signals to andfrom the IRE, and a spectrometer 100 to synthesize the IR signals into aspectra for analysis.

FIG. 26 shows common ATR Configurations: A. triangular prism 316, B.trapezoidal prism 316 and C. ATR geometric principle.

In order to maximize the sensitivity and utility of the ATR, the IRE isoptimized specifically for oral cavity spectral data collection. Boththe shape and the material composition of the IRE affect itsperformance. Materials vary in their refractive index (higher isbetter), their useful spectral range, their reactions with water andother chemicals and their visible transparency. In order to obtain theideal internal reflectance within a high index material it is necessaryto optimize the device with respect to certain importantparameters—namely internal angle of reflectance (φ), the index ofrefraction of the IRE material (n1), and the wavelength range (λ) usedfor the measurement. Also important is the index of refraction of thesample (tissue) (n2).

The goal is to optimize the angle φ, which is affected by the shape aswell as n1 and n2. Fifteen different candidate IRE materials have beenexamined for this application with the best two candidates being diamondand coated silver bromide.

Also important is Dp (depth of penetration), which is the pathlength orthe effective thickness of sample that is interrogated. This variesbased on the magnitude of φ and n1 for the measurement range. In oralcancer applications a shallow penetration (about 1-5 μm) is preferred sothat the IR signal penetrates only the surface tissue layer, where thecancer would reside, and does not pick up deeper tissue that couldcomplicate or interfere with the surface IR signal. Depth of penetrationis very relevant to probe both the surface and sub-surface of theepithelial layer, thereby increasing the sensitivity of the measurement.In addition, extending the optical interaction below the surface helpsto further reduce spectral interference from water in the saliva.

FIG. 27 shows alternative IRE geometries for the prism 316. Geometry Dis preferred for the oral cancer application, where the top surface istargeted for sample interfacing. The key feature of Geometry D is thatthe angles provide an asymmetric beam path where there are two differentsurface angles. This asymmetric design allows the light to enter the IREcloser to the critical angle (i.e. beyond the critical angle light doesnot reflect from the tip back into the return fiber) and hence be ableto penetrate deeper (closer to 5 μm) into the tissue. For comparison,geometry B offers a symmetric angular operation and the depth ofpenetration is predetermined and more shallow. In difference, underGeometry D the reflection at the top surface is controlled by the angleson the sides and the overall diameter of the top surface, allowing forgreat flexibility and options.

There are at least three properties/parameters that influence the choiceof fiber material for umbilical 314 shown in FIG. 25: spectraltransmission range, attenuation (a function of distance/fiber length)and fiber flexibility. Currently, there are three commonly used types offiber materials for the 6 μm to 12 μm spectral region: chalcogenideglass, silver bromide-chloride (mixed halide) and hollow core fibers.The hollow core fibers have a good transmission and spectral range butare not very flexible and have a limited bend radius, which limits theirusefulness when trying to manipulate the probe within the mouth. Thebest match at this time is the mixed silver halide material. It has theflexibility needed for a probe for use in the mouth although it willneed to be properly packaged to ensure that the fiber is not excessivelystressed.

The key for the ATR application is to correctly interface the opticalfibers 314 to the IRE prism 316 to maximize light throughput.Importantly, the QCL spectrometer 100, which produces a collimated 2 to4 mm beam diameter, is better matched to the fiber than an FTIR. Thisfeature along with the inherent high power of the QCL provides a signalto noise ratio (SNR) of 10,000:1 compared to reported SNR values between30 and 150 for similar measurements, using FTIR systems.

FIGS. 28A-28C show three embodiments of the ATR probe tip. FIG. 28A usesa two fiber system. See fibers 410, 412, with an integrated micro videocamera to enable the point of measurement (the lesion) to be viewed bythe examiner; visible light is provided by a third fiber, above theplane of the paper, not illustrated. The camera optics and dual IR fiberadds width to the construction. In this case the reusable probe isdesigned to be able to be sterilized. It uses, preferably, a diamond IREtip 414 in a stainless steel housing, not shown. An estimated overallwidth for such a construction is approximately 5 mm diameter althoughthe effective measurement area on the tissue could be less than 1 mm.

FIGS. 28B and 28C show other embodiments using a disposable tip, whichmay be preferred in certain clinical settings. FIG. 28B shows thecomplete assembly with the fiber 314 and imaging optics 2810, and FIG.28C indicates the disposable components including the sheath s and theIRE prism tip 416. A narrow diameter inner optical assembly issurrounded by an outer jacket or sheath s that is disposable andincludes a disposable IRE 414. The sheath is preferably constructed of asuitable rigid molded plastic, such as PEEK (polyketone). To keep costslow, the IRE 414 is molded out of silver bromide. Silver bromide has theideal optical properties for an IRE vis-à-vis spectral range and indexof refraction. Although silver bromide is insoluble in water, it ispotentially vulnerable to attack by salts and compounds dissolved insaliva. Therefore, this IRE 414 is coated with a sub-micron thickness ofParylene. This ultra thin coating 416 provides excellent surfaceinertness while not interfering with the optical properties of the IRE.

One embodiment is used for detecting cancerous cells using the ATR probecoupled to the QCL spectrometer 100. FIG. 29 is a flow diagramillustrating this method.

In step 2910, the ATR probe 310 coupled to the QCL spectrometer 100 isplaced in contact with the skin of a patient. The surface of the skin isthen scanned with probe 310 in step 2920. In step 2930, the IR spectraof the skin are recorded by the Quantum Cascade Laser based analysissystem 100. In step 2940, the spectra are then compared to a database ofspectral data of known cell types. Based on this comparison, the cellsexamined are categorized as non-cancerous, reactive, dysplastic, orcancerous in step 2950.

In the preferred embodiment, the spectrometer 100 acquires spectraquickly, in less than a few milliseconds. This provides an opportunityto obtain both spatial resolution and temporal resolution of the tissuesurface. If a small contact area such as 1 mm is moved across thesurface under investigation it is possible to obtain differentialspectral data with as little as a 10 μm movement (1% of contact area).By providing spectra for just this narrow spatial area (which would looklike a new moon sliver), the detection accuracy is potentiallyincreased.

The system is used to evaluate of suspicious lesions to importantlocations in the oral cavity, namely (1) Tongue, (2) Lip, (3) Floor ofmouth, and (4) Other (buccal mucosa, upper and lower alveolarridge/gingiva, and hard palate).The “Other” category is grouped becauseit constitutes less than 10% of all oral cancer cases and previousanalyses has suggested that these areas so grouped are spectroscopicallysimilar whereas the first three are a bit more spectroscopicallydistinct.

Detection of Thermal Damage to Composites

The resin of composite materials when exposed to high levels of heat(above 375 degrees F.) becomes damaged and the structural integrity ofthe material is compromised. The level of damage is related to thetemperature that the material is exposed to. The QCL spectroscopy system100 is used to detect composite damage both in a standoff arrangementand with a fiber optic probe to detect damage within drill holes.

Currently, handheld FTIRs are being used to detect this thermal damage.There is a correlation between the absorption of the material in theMid-IR, and its level of damage. Specular reflectance is used to measuremost thermal damage situations (except heavily abraded graphite fibercomposites where diffuse reflectance is used). The bands that changewith thermal exposure are generally between 2000 and 700 cm−1 andusually limited to between 1800 and 1000 cm−1.

The problem with using handheld FTIRs is that it is necessary to be invery close contact with the composite material, the measurement takesabout 1.5 minutes/sample because of the limited amount of light that isreturned to the FTIR, and the spot that is measured is very small.

An embodiment concerns a method for detecting composite damage at astand-off distance using the QCL spectrometer system. Utilizing a QCLabsorption spectroscopy system 100, it is possible to make thesemeasurements at a standoff The amount of light that hits the sample issignificantly higher (on a per wavelength basis) than with an FTIR,which allows for significantly faster measurements. Finally, theeffective spot size that is used with a QCL system is significantlylarger than with an FTIR system, expanding the effective area that istested.

The QCL absorption spectroscopy system 100 is able to detect thermaldamage in composites from a standoff distance between 6 inches and 2feet. In one example, the QCL absorption spectroscopy system 100 usesinfrared laser absorption spectroscopy across a wavelength range of 1000to 1600 cm−1 (or 6-10 μm) to detect differences in the spectra collectedfrom damaged and healthy composite surfaces. These differences aretypically correlated to thermal damage using software data processingalgorithms.

The advantages with standoff, faster measurements, and larger inspectionareas is that a device with these characteristics is much more practicalfor field applications, where very rapidly scanning areas of compositedamage are key.

FIG. 30 is a flow diagram illustrating the method of detecting compositedamage at a stand-off distance using the QCL spectroscopy system 100.

In step 3010, QCL spectroscopy system 100 is aimed at a compositesurface to be tested. The IR spectra are then measured in step 3020. Instep 3030 the spectra are compared to known spectra of the samecomposite lacking thermal damage. A determination is made as to whetherthe spectra are significantly different in step 3040. If they are not,then it is determined that no thermal damage is present, as seen in step3050. If they are significantly different, then the spectra is furtheranalyzed in step 3060 to determine if thermal damage is present and theextent of thermal damage.

Detecting Thermal Damage in Composite Drill Holes

A more specific application of the QCL absorption spectroscopy system100 in detecting thermal damage in composite materials is the use of thesystem with a fiber optic probe to detect potential thermal damage todrill holes in composite materials.

This technique detects the thermal damage inside the drill holes. Acustom fiber optic probe is inserted into the drill hole, illuminatesthe sides of the hole, and couples the reflected light back into thesystem 100.

It is important to detect thermal damage in drill holes. If the drillbit overheats, the section is usually cored out and a larger bolt isused, without verifying whether there was damage.

There are nondestructive testing techniques that are being explored forthis application, such as ultrasound. However, the problem is thatalthough these other techniques can be used to detect structural damage,such as delamination, they cannot detect polymer degradation that has achemical rather than a physical signature.

FTIR has proven effective in detecting some cases of thermal damage tocomposites. However, it is not possible to couple enough light from anFTIR into the drill hole, to be able to get a signature that can be usedfor analysis. This is because the source of an FTIR is incoherent andlarge (e.g. globar) and, hence, it cannot efficiently be coupled into afiber probe.

In contrast, in the QCL absorption spectroscopy system 100, the sourceis a Quantum Cascade Laser (QCL), which is a very bright (high spectralradiance) source, which means that it can be coupled with very highefficiency into a hollow silver halide fiber, for example.

The sizes of the drill holes are between about ½ inch to 3/16 of aninch. The depth of the holes in composite are ¼ inch to ¾ inch. However,because of titanium above or below the hole, the probe needs topenetrate through a hole that can be between 1 to 1¼ inches in depth.The key issue is making a fiber probe that will be small enough to enterinto the holes and illuminate the composite material and then couplethat light back into the fiber.

In one implementation, a fiber link to a probe is silver halide orsilica hollow core fiber (see FIGS. 31 and 32). The system will bedirectly coupled to the fiber 2200 which ends in a probe 2202 (FIG. 33).

There are various potential geometries for the probe 2202. FIGS. 34-37show some potential examples. Each of these probes 2202 couple lightreceived from the QCL absorption spectroscopy system 100 to the sidewalls of the drill hole via a turning mirror, prism or conical reflector(axicon). FIG. 37 is ray trace for the axicon implementation. Amicrolens 2204 improves coupling between the fiber endface and theturning element. In some examples, returning light from the hole sidewalls is returned to the spectrometer 100 via the same fiber 2200. Inother examples light back to the spectrometer is carried in a secondfiber.

FTIR Microscope using QCL Spectrometer

In a conventional FTIR microscopy, the FTIR spectroscopy system includesa relatively large, broadband, mid-IR source, the emission of which goesthrough an interferometer and then into an infrared (IR) microscope. Thelight hits a sample and then that light is either reflected ortransmitted through the sample onto a detector. As the moving mirror ofthe interferometer is shifted, the amplitude information on the detectoris converted into spectral information though the use of a Fouriertransform.

The issue with the existing approach is that the broadband, mid-IRsource is a physically large source, so its diffraction limited spot isalso very large. In order to look at small samples, rather than focusingthe light down to those small spots, the light is apertured eitherbefore it hits the sample or before it hits the detector. The apertureblocks the light outside the field of interest. Therefore, the amount ofenergy hitting a small section of the sample of interest is a tinyfraction of the light initially entering the microscope. By the time thelight hits the sample, it can be orders of magnitude less than the lightthat enters the microscope.

Furthermore, the light from the broadband mid-IR source has significantpower (i.e., 250 milliWatts), but it is broadband, so if the persondoing the measurements has only a few wavelength ranges of interest,there is no way to parse this out optically.

There are two problems with the FTIR microscope system. First, the useris dependent upon scanning the whole spectral range with an FTIR, to getthe desired spectra of interest, which takes time. Second, the detectoris often close to saturation from this mid-IR source, and further issaturated with wavelengths that are not of interest to the user. Thisdiminishes the dynamic range of the detector in the wavelengths ofhighest interest.

The key practical problems with the existing approach include:

1. Measuring the spectral information on small sample sizes (i.e., 10micrometer×10 micrometer spots or lower), often requires longmeasurement times to integrate enough light to obtain useful spectralinformation. This is a particular problem, with regard to time, whenattempting to collect high spatial resolution measurements on arelatively large sample, where moving a stage from spot to spot isrequired to cover the entire sample.

2. Conversely, the user may choose severely degraded spectralinformation or spatial resolution (larger sample spots) to speed up themeasurements.

3. It is difficult to obtain reflected spectral information on samplesthat are highly diffusive or absorbent.

4. It is difficult to obtain transmitted spectral information on samplesthat are relatively thick.

The advantage with a mid-IR semiconductor laser (QCL) based microscopeis that more energy is delivered to a small spot of interest. This isbecause the laser is more powerful than the broadband, mid-IR source,but more importantly, the laser delivers a much smaller diffractionlimited spot. So for many samples, there is no need to aperture thelight. In cases where aperturing the light is required, the amount lostis much less than with the large than for a broadband Mid-IR source.This is especially true for a semiconductor laser in which the gain chipsupports only a single spatial mode or only a few spatial modes, whichtranslate to small beam sizes.

The present system combines a microscope with a widely tunable mid-IRlaser. The advantage with this type of laser is that it is possible toobtain spectral information from the fingerprint region, which providesmuch more pronounced spectral peaks than in the NIR or visible. Thewidely tunable mid-IR absorption spectroscopy device described aboveprovides the enabling technology that makes a mid-IR laser basedmicroscopy system possible.

In one embodiment of the system, the tunable laser is pulsed at awavelength, the light enters the microscope and then is eithertransmitted through a sample or reflected off of the sample onto adetector. The detector correlates the light that it collects with thewavelength of light that was transmitted by the laser. Then the laserpulses at the next wavelength in a range and the process repeats manytimes to build up a full spectrum of the material of interest. In amicroscope where there is a scanning stage the electronics from themid-IR laser system would be tied to the moving stage, so that thesample could be moved to the next point once the spectral information iscollected.

The laser based system has the following advantages:

1. Light can focused onto small spots providing higher power on smallsamples, which translates into higher a signal to noise ratio (SNR).This means either higher quality spectral data or less time required tomake a measurement.

2. There is more light on the sample, so that samples that do not returnmuch light in conventional systems can be measured effectively using alaser based system.

3. The laser can be set to tune across a specific wavelength band ofinterest, speeding up measurements for applications, where looking atbroadband spectra is not needed.

Additional configurations include a single detector, a linear detector,or a focal plane array. Also, it is possible to inject the laser beaminto the FTIR rather than into the microscope directly.

Conventional FTIR microscope imaging systems are made from the ground upand do not use conventional microscopes as the basis for construction.This has been required to accommodate and optimize the interfacing withthe FTIR instrument, to reduce ambient interferences, and to accommodatethe mechanical parts required in the physical scanning of the sample onthe microscope stage. In addition, they require the use of sophisticatedoptical systems incorporating expensive Cassegrain lenses, and there isthe need for the use of liquid nitrogen cooled detectors, which are bothlarge and expensive to purchase and maintain.

FIG. 38 shows a QCL microscope system. It is much simpler andincorporates three basic elements: (1) a conventional light microscope510, although Cassegrain objectives are used in some implementations forthe 6-12 micron spectral range, (2) the QCL spectrometer 100 describedabove but with a detector array such as a MEMS-based microbolometerthermal detecting array, and (3) an x-y scanning stage 512 to scan thesample under the optical microscope 510 and the tunable signal from theQCL spectrometer. The spectral tuning range of a QCL spectrometer 100 ispreferably 6.0 to 12 micrometers, which covers adequately the spectralregion that is the most useful for medical diagnostics. Because of therelatively high power of the QCL, expensive, cooled detectors are notrequired. Furthermore the expensive optical systems associated with FTIRsystem are eliminated. Importantly, the QCL spectrometer is orders ofmagnitude faster than conventional FTIR imaging systems because the QCLsystem uses an extensive array to produce the image within minutes incontrast to conventional FTIR systems that scan the image much moreslowly, often taking hours to produce a result.

FIG. 39 shows an alternative QCL tunable laser 110 configuration inwhich the grating tuner is replaced with a Fabry-Perot tunable filter510 and a discrete back cavity mirror 512. This laser configurationreplaced the grating tuned versions described previously in embodimentsof the present invention;

Also shown are four micro electrical mechanical system (MEMS)Fabry-Perot tunable filter configurations. Generally, the device layer(d) thicknesses are about 10 micrometers, the buried oxide (o) thicknessis 1 micrometer, and the wafer (w) thickness is 400 micrometers. Antireflection coatings AR are used to improve coupling into the opticalcavity defined by highly reflecting layers HR.

Identification of Materials Using Automated Assessment of IR SpectralData

FIG. 40 shows a method for using the QCL spectroscopy system 100 inidentifying an unknown substance by automated assessment of spectraldata.

In order to identify an unknown substance by infrared spectralmeasurements, it is necessary to step through a series of measurementscenarios and to narrow down the options that exist for the generationof the spectral signature. These are grouped into the following subsets:an initial or first-pass assessment of the data, the determination andcharacterization of noise sources, the characterization of the spectralbackground (what is a constant and what is a systematic variable), thedifferentiation of the analyte of interest (the unknown) from thebackground and how to determine if the unknown material is present in amixture. These scenarios are often interrelated and one step in theprocess can be highly dependent on another.

1. First-Pass Assessment

The first-pass assessment is made in step 4010. Here, the light level isvery important for the first evaluation of the spectral signal as it caninfluence the way that the spectroscopy system 100 is used and theoverall significance of the spectral signal. The light level caninfluence the efficiency of how the full digitization range of thedetector system is used. The signal is digitized from zero light on thedetector to full light on the detector, and this is governed by thedetector response (and linearity) and the analog to digital converterused for the digitization. One assesses how much of the signal carriedthe useful information, its numerical significance, and how well thenoise is represented. In order to characterize the noise correctly, inone of the important steps in the overall process, the noise isaccurately recorded and represented.

Then, the basis for other variations in the signal are determined. Oftenthese variations are influenced by the measurement system itself and theway that the light is captured. The sample itself can also be changingand those changes can range from the texture of the surface to changesin the material composition or morphology at the sample surface asviewed (for solids and liquids). When a spectrometer is viewing achanging field of information, the light level is a fundamental elementas indicated above, and in order to capture the signal and its nuancesthe resolution and linearity of the measurement system become importantfactors. In the final steps the data are normalized for comparisonpurposes and it is important that the raw data were captured asaccurately as possible.

The spectral content of a sample is influenced by the method used tocollect spectral data, including the physics of the light interaction atthe surface of the sample and the absorption characteristics of thesample and its substrate. It depends on whether only the surface of thesample/substrate interacts or the bulk of the material interacts. Whenthe interaction is purely on the surface the refractive index of thematerial becomes a dominant factor, whereas if penetration into the bulkoccurs then the spectral content is governed by absorption. In manycircumstances it is not clear cut, and both mechanisms occur giving riseto a mixed mode of interaction. The result is a complex signal that ischaracteristic of the material but does not conform to an immediatelyrecognizable signature.

As described above, there are many methods used for the sampling ofmaterials by QCL spectroscopy. The method required for the measurement(contact or non-contact) tends to dictate the method selected. Solidsand liquids may be sampled by methods that involve sample contact, suchas with the ATR probe, or otherwise, such as stand-off. In the formercase an absorption-like signature is obtained. In cases of stand-offmeasurement the mixed mode scenario discussed above is determined bywhether the measurement involves a specular (mirror-like) or diffusemeasurement from the sample. For gases, the mode of measurement is inmost cases absorption based, whether the gas is contained in a gas cellor is free in an open path scenario. The main exception is where anemission mode of measurement is made.

In the end, the spectrum of a sample is recognized and identified by thepresence of characteristic signatures. Ideally these are well definedsignatures that contain peaks related to the specific chemical speciesthat are to be detected. In mixed mode scenarios the appearance of thepeaks may be distorted, but if the signature is representative of thematerial under investigation then even distorted data should be able tobe correlated back to that material(s) of interest. For automatedprocessing of the data, the presence and nature of “peaks' within thespectral data are determined. Algorithms are capable of handlingnon-standard spectral signatures and waveforms.

2. Determination of Noise

In step 4020, the noise is determined. In a practical system, noise isdefined as information that is varying on a random or systematic basisthat is not directly linked to the signal of interest (the spectralsignal). Both signals can be varying, and it is important todifferentiate and separate both signals. Note that noise can be presentin the signature that originates from a background or interference. Itis important to isolate this component in order to obtain the spectralinformation of the target of interest. Spectral noise from thebackground is treated the same as the sample spectrum in collection andis treated differently at the end of the identification process.

Electronic Noise—random/systematic—Random noise is usually the easiestnoise source to handle if it is truly random. If there are alsosystematic noise sources in a system they are identified and selectivelyremoved. Such signatures are identified and corrected prior to thespectral measurement.

Sample Noise—mixture of random and systematic—This is more difficult toidentify and handle. An example covered above is where there is morethan one mode of measurement of where the signal level from the sampleis fluctuating. This is handled in the data collection process by theuse of auto-correlation methods, and in spectral matching to known andexpected signatures. Signals that are correlated are separated from thenon-correlated signatures.

Spectral Interferences—systematic—in this situation the signal is firsttreated as spectral data. One then monitors the signal to see if it ischanging. Spectral interferences are treated as backgrounds. If a signalis changing then it is important to determine how it is changing and isit is systematic or random. Systematic signals are extracted by crosscorrelation methods and these are combined with spectral differentiationprocedures to separate the background from the sample signature. Thespectral signatures from interferences that can be identified are usedlater to both differentiate and quantitate the relative amounts ofsample versus background in the overall signature.

3. Background Assessment

In step 4030, a determination of the background is made. Preferably thisdetermination of background is made by correlation methods. This islinked to the assessment discussed above. In a dynamic measurementsituation the current spectral signature is compared to the mostprevious signature, and other previous signatures. The signature of thebackground is assumed to be the most constant and is used for separatingbackground from the signature of a different material. In a staticmeasurement situation the background is normally determined and recordedseparately prior to the actual measurement.

Detection of background changes—In a dynamic measurement when abackground has been identified as a background, it is compared to themost current signatures by correlation and closeness of fit methods.Differences observed are then linked to the presence of anothersubstance or chemical species. The background signatures are highlycorrelated, and a loss of correlation signifies the presence of anothermaterial.

Detection of contamination—in a dynamic situation, a change inbackground is detected from the spectral signatures, which are firstcorrelated to the established background. A loss of correlationindicates the presence of contamination. The spectral contamination isthe differentiated from the background by the use of spectral fitting(such as least squares fitting) or spectral subtraction methods. Oncethe spectral signature of the contaminant is extracted it is furthercharacterized by comparison to known signatures of target compounds.

4. Identification of Materials

The materials are then identified in step 4040. This process includes aseries of substeps.

Characterization of the background—the background of a spectrum iseither pre-determined or determined in real-time as discussed above. Insome cases it is important to characterize the background because ifidentified, it is used later to differentiate it from a contaminantspectrum that is measured in the presence of that background. If thematerial (solid, liquid or gas) has a characteristic signature then itcan be matched to a stored library of compounds and substances.

Determination of the spectrum type—absorption vs. refractive index—theimportance of spectrum type was mentioned earlier. If the spectrum ismixed mode then it will be distorted. If the type of distortion isknown, then algorithms, such as the KK-transform, are applied to convertthe spectral data into a more consistent and recognizable format.

Peak-based identification—digital mask—this assumes that identifiablepeaks can be discerned. If they can and the peak positions can bedetermined, then a quick sort and identification will be performed bythe use of a simple binary mask. In this case the presence or absence ofa peak is determined by simple Boolean algebra. This can be assessed asan absolute match (presence and absence weighted) or a positive match(just based on presence). The identification is then made based on a setof binary codes stored for known substances.

Peak-based identification—peak table—this is a more discriminatingmethod of identification than the simple binary approach, where peakheight (or relative peak height) is taken into account. Also, peak tablebased algorithms can be designed to accommodate peaks shifts caused bychemical interactions or physical interactions, and other parameters,such as width may be used as a differentiating factor. Often an exactmatch to both peak position and height is sufficient for an absolutematch, as long as there are a statistically significant number of peakspresent. Fuzzy logic is applied peak matching methods in some examplesto accommodate spectral shifts and variances caused by physical,environmental or chemical interaction effects.

Spectral matching based on correlation—a wide range of correlationmethods exist, and these range from cross-product type correlations togoodness of fit methods. Dependent of the nature of the spectrum (broadfeatures vs. narrow, well defined features) the goodness of fit methodsare often more differentiating and are better for separating minordifferences in spectral data. Note that for absolute identifications,correlation methods that can be weighted by the presence and location ofpeaks are often required.

5. Handling Mixtures

Treating mixtures as single entities—mixtures can be stored in a libraryand compared directly to the unknown. The unknown is then identified asthat mixture or a close fit to that mixture. For example, a formulatedproduct is most likely to be a mixture on chemical substances, with oneor two being dominant. In terms of identification it is often morepractical to identify the material as that “product” rather than attemptto identify the components, unless the intent is to identify and measurethe amounts of the major components. If the material is to be measuredas a single entity then its ID can be based on its overall spectrumusing methods described above. If quantification is required, thensimple “absorbance” based Beer's Law measurements or simple leastsquares fitting can be applied.

Simple resolution of mixtures—Determining what is present in a mixturecan be performed by using a simple peak-based or binary match wherepositive, rather than absolute presence of peaks/features is used in thelibrary match. If a major component is identified, then one approach isto subtract out the major component spectrum and then re-apply thespectral search to the spectral residue (following subtraction). Usingthis approach other components of mixtures can be identified and thiscan be performed at least twice from good quality spectral data. Beyondtwo or three applications of the subtraction method the residual databecomes too distorted by artifacts and noise to be useful in furthersubtractions. In terms of quantitative measurement, if scaling isrequired in the spectral subtraction procedure, then the amount ofscaling applied can be used to provide a quantitative estimate of therelative amount present of that particular component. If the componentsare sufficiently well identified, then simple Beer's Law methods areapplied, and a matrix based solution may be used in cases of significantspectral overlap of the individual components.

Multivariate modeling of mixtures—If a mixture is not well characterizedthen methods based on multivariate modeling are preferably used. Theseare often difficult to manage and usually require multiple referencespectra that represent the variances of composition within the materialof interest. This requires a good data base of reference substances.Factor analysis may be used as a method to look for similarities inmaterials and to extract spectra of common spectral significance.Methods considered can range from simple MLR (multiple linearregression) to neural network approaches.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the invention.

What is claimed is:
 1. A spectroscopy system comprising: at least twolaser modules, each of the laser modules including a laser cavity, aquantum cascade gain chip for amplifying light within the laser cavity,and a tuning element for controlling a wavelength of light generated bythe modules; combining optics for combining the light generated by theat least two laser modules into a single beam; and a sample detector fordetecting the single beam returning from a sample.
 2. The spectroscopysystem of claim 1, further comprising three of the laser modules.
 3. Thespectroscopy system of claim 1, wherein the tuning element comprises agrating.
 4. The spectroscopy system of claim 1, wherein the tuningelement comprises a Fabry-Perot tunable filter.
 5. The spectroscopysystem of claim 1, further comprising projection optics for projectingthe single beam to a sample.
 6. The spectroscopy system of claim 1,further comprising a sighting laser and a housing with attached handle,wherein the laser modules are contained within the housing.
 7. Thespectroscopy system of claim 6, wherein the system operates on 30 Wattsor less.
 8. The spectroscopy system of claim 6, further comprising asoil marking device for the detection of disturbed earth.
 9. Thespectroscopy system of claim 1, wherein the sample detector is separatedfrom the laser modules.
 10. The spectroscopy system of claim 1, furthercomprising retroreflectors, wherein the single beam is projected to theretroreflectors and then returned to the sample detector.
 11. Thespectroscopy system of claim 1, further comprising a gas cell and aportable hand-held housing, wherein the laser modules and the gas cellare contained within the housing, the single beam analyzing gas in thegas cell.
 12. The spectroscopy system of claim 1, further comprising aportable housing, a fiber optic probe and a fiber optic cable, whereinthe fiber optic cable connects the spectroscopy system to the fiberoptic probe.
 13. The spectroscopy system of claim 12, wherein the fiberoptic probe is a grazing angle probe.
 14. The spectroscopy system ofclaim 12, wherein the fiber optic probe is an attenuated totalreflection probe.
 15. A quantum cascade laser microscopy systemcomprising: the spectroscopy system claimed in claim 1, a lightmicroscope for projecting the single beam onto the sample, and an X-Yscanning stage for scanning the sample under the microscope.
 16. Thequantum cascade laser microscopy system of claim 15, wherein thedetector is a linear detector or a focal plane array.
 17. The quantumcascade laser microscopy system of claim 1, wherein a spectral tuningrange includes 6 to 12 micrometers.
 18. The spectroscopy system of claim1, wherein the tuning element comprises a fixed grating and amicroelectromechanical system mirror that scans light from the quantumcascade gain chip over the fixed grating.
 19. The spectroscopy system ofclaim 1, wherein a position of the mirror is used to determine awavelength of light generated by the laser module.
 20. The spectroscopysystem of claim 1, wherein the sample detector comprises a twodimensional microbolometer array.
 21. A spectroscopy system comprising:a laser module including a laser cavity, a quantum cascade gain chip foramplifying light within the laser cavity, and a tuning element forcontrolling a wavelength of light generated by the modules; projectionoptics for directing the light generated by the laser module onto asample; collection optics for collecting light from the sample; and asample detector for detecting the light collected by the collectionoptics.
 22. A spectroscopy system comprising: a laser module including alaser cavity, a quantum cascade gain chip for amplifying light withinthe laser cavity, and a tuning element for controlling a wavelength oflight generated by the modules; collection optics for collecting thelight from the sample; and a sample detector for detecting the lightcollected by the collection optics. a spectroscopy reference, whichduring a calibration process, is inserted into the light generated bythe laser module to reflect the light to the sample detector.